Oscillograph galvanometer



May 14, 1929. J, w LEG@ 1,712,570

OSCILLOGRAPH GrALVANOMETERA Filed Jan. 2'7, 1925 INVENTOR WITNESS 1 r 323437 /5 Jaso/f /f/ Q99 Patented May 14, 1929.

UNITED STATES VPATENT orifice.

JOSEPH W. LEGG, OF WILKINSBUBG, PENNSYLVANIA, ASSIGNOB TOWFS'IINGEEOUSEy ELECTRIC da MAN'UFAGTURING'l COMPANY, .A CORPORATION OFPENNSYLVANIA.

OSCILLOGRAPH GALVANOMETER.

Application led January 27, 1925. serial No. 5,166.

My invention relates to galvanometers and particularly to galvanometersfor use in oscillographs.

One object of my invention is to provide a galvanometer that shallcomprise a permanent magnet constructed of a single homogeneous mass ofmagnetic material and of such coercive :force and such small dimensionsas compared with the magnets of galvanometers heretofore employed forthe same purposes, as to render the galvanometer extremely compact inconstruction, light in weight and eli'ective to indicate the phenomenaof commercial and other electric circuits.l

Another object of my inventionis to provide a galvanometer that shall berugged and 'durable in construction and economical to manufacture.

Another object of my invention is to provide a galvanometer that shallpermit an oscillograph, for which it is adapted, to be more lreadilyportable than oscillographs of the prior art.

Another object of my invention is to provide a galvanometer comprising apermanent magnet that shall be so shaped as to materially increase theeii'ectiveness of. the instrument.

and well-known types, it has been customary to employ permanent magnetsconstructed of materials having low coercive orce, and otherobjectionable characteristics. A magnet having low coercive force limitsthe use ot galvanometers to the measurement of relatively smallcurrents, such'as laboratory-test galvanometers.

The objection has been overcome, to a very au limited extent, byemploying a plurality of magnets or a plurality of large magnets havingrelatively large pole ends but even these measures have not renderedpermanent .magnets suitable for use in oscillographs having anyconsiderable variety of application.

in oscillographs for measuring'transient and current phenomena ofcommercial and other circuits, it is necessary to have currents otcertain relatively large magnitudes te traverse the galvanometerelements. lt has been usual to employ electromagnets tor controlling themovements of the elements. ln such structures, the electromagnets havebeen relatively heavy and expensive and have been Heretofore, ingalvanometers of the usual character having such shape, dimensions andother characteristics as to render the galvanometer an improvement, invsubstantially all of its features, over similar galvanometersheretofore employed.

A magnetized structure or member constructed in accordance with myinvention preferably comprises cobalt steel having a compositionsubstantially as outlined in U. S. Patent 1,678,001, issued to P. H.Brace, J uly 24.-, 1928. It shall be understoodz however, that myinvention is not to be limited to the utilization of material such asdescribed in, v80` netizable material having the desired degree j theaforesaid Brace patent, since any mag` ot coercivity may be utilized inlieu of the material described in said Brace patent.

However, the particular shape, size, disposition and relation of themagnet to other elements herein described, are important elements in theproduction of the improved galvanometer oi my invention, and it is thesefeatures, in the combinations set "forth, which I claim as new.

Figure 1 ot the accompanying drawings is a plan view ot a galvanometerstructure of my invention, embodying a plurality of in dividualgalvanometer unit-s, one of which is shown in section,

' Fig. 2 is a side elevational View of the device showii in Fig. l, withone of the galva nometer units similarly shown in section, and

Fig. 3 is a sectional view, taken through one oit the galvanometer unitsot the other figures, at right angles thereto.

The device comprises, in general, a base member or plate l, verticalgalvanometersupporting plates Q, a rear-wall plate 3 and a plurality oigalvanometers l. The plates 1, 2 and 3 are preferably constructed otrelatively hard insulating material, such as fibrous material,impregnated with a binder,

that are provided with rabbet joints 6k and 7 and are suitably heldtogether, as by screws 8.

Each galvanometer 4 comprises a liquidtight casing or well structure 10that is constructed of a single homogeneous mass of material preferablyinsulating material, and is provided with a cover member 11.4 Each wellstructure 10 is pivoted between adjacent pairs of the members or plates2 by trunnion screws 12. Spacing flanges 14 on the screws 12 aredisposed between the well structure 10 and the partitions 2.

Each well structure 10 is provided with a main or upper interior recess15Vhaving a downwardly projecting opening or recess 16 to provide ashoulder or shelf -17 between the top and bottom ends of the structure10.

A permanent magnet 18, of substantially annu ar shape and having aneccentric opening 19, is'mounted on the shoulder 17 and secured inposition thereon, as by screws 20. A relatively narrow slot 22isprovided in the perimeter of the magnet 18 to'provide concentrated poleends 23 that are disposed opposite an opening or window 24 in the sidewall ofthe well 10. A lens 25 and a light shield 26 are provided overthe openingl 24 in the well 10, the lens 25 being slightly inclined toprevent reflection.

The gal-vanometer element comprises an elongated lamentary conductor 29that is doubled back on itself to have its adjacent ends attached toextensions 27 .of terminal posts 30 and a looped intermediate portion orend 31 disposed around a pulley 32. The pulley 32 is mounted on a lever34 that is pivoted to a depending portion 35 of a stationary supportingstructure 36, as by a pin 37, and adapted to be held under predeterminedtension by a spring 39 which extends between a pin 40 at one end of thelever 34, and screw 42. The screw 42 is adjustably mounted in a threadedprojection 43 on the supporting structure 36. The supportin structure 36 is positioned on the cover mem er 11 by a centering post 44.

The filamentary conductor or conductors 29 may extend across the window24 between bridging posts 45 on the supporting structure 36 and carryVa'mirror 47 for eo-operation with a light source, a vpolygon of mirrorsand a photographic chart (not shown).

The m1rror-47is-adapted for adjustment about a vertical axis by arack-and-screw device in which the rack 51 is secured to the supportingstructure `36 and the screw 52 is v journaled in the cover member 11..Adjustment of the mirror 47 about a horizontal axis is 'efected' throughthe medium of an adjusting device'54, which com rises lateralprojections and 56;on the and on the structure 10, respectively, and anadjusting screw rod 57, in a -well known manner. l Injtheabove-described structure, each galack-wall member 3` vanometer 4 is aself-contained unit, in contradistinction to previous oscillographgalvanometers in which the controllin kelectromagnets are inter-relatedor in whicii a single powerful electromagnet supplies flux to separatepairs of pole pieces for each galvanom eter element.

So far as I am aware, the structure herein set forth is the first inwhich a single homogeneous permanent magnet member of such compactnature and eiiective operation. has been emplo ed or in which the otherparts are adapte to receive such ma net. This magnet, not only by virtueof t e material of which it is composed, but also, by reason of itsannular shape and other features is, so f ar as I am aware, moreeffective .than any previous permanent magnet that has been employed forsimilar purposes. Further, siee the other parts of the alvanometer areadapted tol co-operate wit i the im roved magnet, an instrument isobtained which embodles combinations of elements that are different fromthose of the prior art and which render the instrument an improvementover the old combinations in nearly every feature.

One im roved function provided by my invention 1s a bodily movement ofthe magnet 18,' as a whole, with the galvanometer 4 when the latter istilted about its horizontal axis, thus avoiding separation of relativelymovable magnetic members and,l thereb materially decreasing thereluctance of t e magnetic circuit.

Making the magnet 18 of annular shape also,reduces the space occupied bya given quantity of the magnetic material and facilitates manufacture ofthe magnet.

By making the main central openin 19 through the magnet 18 also annularan eccentrically disposed relative to the outer annular surface,together with the relatively -narrow air gap '22 and parallel pole-endsurfaces 23 from which the adjacent side and end surfaces slope towardthe main body surfaces, a magnet is provided which ensures substantiallymaximum fiux efficiency adjacent to .the galvanometer element 29.

The structure, in which the mainrcess 15 and the downwardly projectingrecess 16 are provided and the magnet 18, conforming to the main recess15, is mounted on the shou der 17 and enclosed by the well structure 10,facilitates manufacture and assembly, ensures economy of space andmaterials and in general, renders the device of my invention animprovement in the art.

While I have shown and desc ibed a parlticular form of ymy invention, canges may 'be effected therein without departing from the spirit andscope thereof, as set forth in the appended claims.

In the appended claims, the expression chrome permanent magnet steelshall be understood as referring to chrome steel of the type ordinarilyutilized in electrical instruments for forming a magnetizable structure,the aforesaid chrome steel ordinarily comprising approximately 2% ofchromium and 1% of carbon.

l claim as my invention:

l. A portable-oscilloigraph galvanometer comprising a well structure,and a highperiod vibratory elementand a control magnet thereforboth-disposed entirely Within said Well structure. t

2."The combination with a supporting structure, of a `galvanometercomprising a movable element 'and a control magnet for said movableelement, said galvanometer, including said movable element and saidcontrol magnet, being mounted on said supporting structure and movableas a unit in different angularly-related directions relative thereto toadjust the position of the movable element;

3. The combination With a supporting structure, of a galvanometercomprising a Well structure movable in dierent angularlyrelateddirections relative thereto, a movable galvanometer element disposed inthe well structure and a control magnet for the galvanometer elementcarried by the movable.

' Well structure.

1l. The combination With a supporting structure, of a galvanometercomprising a Well structure mounted on' said supporting structure andmovable in different angularlyrelated directions relative thereto, and amovable galvanometer element and a control magnet for the galvanometerelement disposed in said Well structure.

5. A galvanometer comprising a Well structure, a galvanometer element,an elongated supporting structure for said element disposedlongitudinally in said well structure, and a permanent control magnetdisposed in said Well structure and having pole-end portions embracingan intermediate portion of the galvanometer element. p

6. A. galvanomcter comprising a Well structure having an intermediateshoulder portion therein, a galvanometer element, 'a supportino'structure for said element disposed longitudinally in said wellstructure on opposite sides of said shoulder portion, and a permanentcontrol magnet positioned on saidrshoulder and havingpole-end portionsat opposite sides of said element.

7 A galvanometer comprising a cylindrical permanent magnet, a wellstructure `having a main cylindrical recess to snugly receive saidmagnet and an otlfset recess extending downwardly from said main recess,a galvanometer element and a support for the element, said magnetsurrounding said support between said recesses.

8. The combination with a deflecting system freely responsive tofrequencies of the order of 3000 cycles per second and including alight-reflecting mirror, of means for actuating said detlecting systemcomprising a permanently magnetized structure the coercive force ofwhich is several times greater than that of chrome permanent magnetsteel.

9. The combination With a casing, of a deflecting system freely andsubstantially uniormly responsive to frequencies ranging upwardly to3000 cycles per second, said system including a light-reflecting mirror,and a magnetizable structure comprising a permanently ma netized memberdisposed entirely Within sai casing for actuating said deecting system.l

l0. The combination with a casing, of a deflecting system freelyresponsive to frequencies of the order of 3000 cycles per second andincluding a light-redecting mirror, and a magnetizable structurecomprising a permanently magnetized member disposed entirely Within saidcasing tor actuating said deiiecting system, the coercive force ot' saidmagnetized member vbeing several times.

greater than that of chrome permanent magnet steel.

In testimony whereof, I have hereunto subscribed my name this 22nd dayof January,

J OSEEH. W. LEGG.

